Phosphonate-Functionalized Polycarbonates Synthesis through Ring-Opening Polymerization and Alternative Approaches

Well-defined phosphonate-functionalized polycarbonate with low dispersity (Ð = 1.22) was synthesized using organocatalyzed ring-opening polymerization (ROP) of novel phosphonate-based cyclic monomers. Copolymerization was also performed to access different structures of phosphonate-containing polycarbonates (PC). Furthermore, phosphonate-functionalized PC was successfully synthesized using a combination of ROP and post-modification reaction.


Introduction
In the last decades, phosphorous polymers have been widely used in a variety of applications, including dental, energy, and oilfield applications [1][2][3][4]. Owing to their thermal stability properties, phosphonate-based polymers have become some of the most desired flame-retardant materials [5][6][7]. Furthermore, due to the high affinity of phosphonic acid with metallic ions, phosphonate-based polymers have also been transformed into phosphonic acid forms for water purification [8]. To date, the majority of these polymers have been obtained by incorporating the phosphonate group into macromolecular chains via the conventional or controlled radical (co)polymerization of various phosphonatecontaining vinyl monomers [9][10][11]. As a result, these materials consist of vinylic polymer backbones that are difficult to degrade. This may be a significant concern for the environment or (bio)applications. To address this issue, there are a few examples of the synthesis of phosphonate-containing biodegradable polymers. For example, Ho and coworkers have reported the simple synthesis of well-defined phosphonate-terminated poly(ε-caprolactone) (PCL) using the organocatalyzed ring-opening polymerization (ROP) technique and phosphonate-containing hydroxyl molecule as the initiator [12]. Using a similar strategy, other phosphonate-terminated biodegradable polymers such as polylactide (PLA) and polycarbonate (PC) were also successfully synthesized [13,14]. In these studies, the phosphonic acid-terminated polymers were produced by dealkylation of the phosphonate group and then grafted onto the surface of oxide metal nanoparticles for various applications. While the synthesis of phosphonate-terminated biodegradable polymers has been thoroughly described, the introduction of pendant phosphonate groups into biodegradable polymers has rarely been reported. Thus, the synthesis of phosphonatefunctionalized biodegradable polymers remains a significant challenge.
Owing to their biodegradability and biocompatibility, polycarbonates are considered as one of the most important biomaterials [15]. Recently, functional polycarbonates bearing different chemical functionalities have been utilized in various applications, including drug delivery, antimicrobial applications, and tissue engineering applications [15][16][17]. Although many functional PC have been synthesized, the synthesis of phosphonate-functionalized PC is still unknown. To our knowledge, only one attempt has been made to graft the

High-Resolution Mass Spectrometry (HRMS)
Experiments were performed using a Synapt G2 HDMS quadrupole/time-of-flight (Manchester, UK). Samples were introduced at a 10 µL min −1 flow rate (capillary voltage +2.8 kV; sampling cone voltage varied between +20 V and +60 V) under a desolvation gas (N 2 ) flow of 100 L h −1 heated at 35 • C. Accurate mass experiments were performed using reference ions from PPG, PEG, or CH 3 COONa internal standard. All the samples were dissolved in methanol doped with 3 mM ammonium acetate before analysis. Data analyses were conducted using MassLynx 4.1 programs provided by Waters.

Fourier-Transformation Infrared (FT-IR)
Spectra were recorded using a Perkin Elmer Spectrum Two FT-IR Spectrometer with an ATR accessory.

Nuclear Magnetic Resonance (NMR)
1 H, 13 C, and 31 P NMR spectra were recorded on a Bruker AC 400 MHz using deuterated solvents such as CDCl 3 or acetone D6. Chemical shifts were reported in parts per million (ppm) calibrated using residual non-deuterated solvent as internal reference (CDCl 3 at δ 7.26 ppm ( 1 H NMR) and δ 77.16 ppm ( 13 C NMR); acetone D6 at δ 2.05 ppm ( 1 H NMR) and δ 29.84 ppm ( 13 C NMR)). Polymers were characterized using the PL120 system (Polymer Laboratories, Church Stretton, UK), equipped with an injection valve (50 µL loop volume), a column oven, and a refractive index detector thermostated at 50 • C. The stationary phase was a set of two linear M PSS GRAM (300 × 8 mm) columns (PSS, Mainz, Germany). The eluent was DMF supplemented with NaNO 3 (50 mM) and delivered at a 1 mL/min flow rate. Samples were solubilized in a mixture of the eluent and toluene (flow marker) at 0.25 vol.% and at a concentration of 0.25 wt%. Polymer equivalent number-average molar masses (M n,SEC ) and dispersity (Ð) were calculated using a poly(methyl methacrylate) (PMMA) calibration curve based on PMMA standards from 0.885 to 520.0 Kg·mol −1 (Agilent, Santa Clara, CA, USA).

Synthesis of 2-(Dimethoxyphosphoryl)ethyl 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoate (3)
The phosphonate compound 2 (16.0 g, 0.0516 mol), resin Dowex ® 50WX8 hydrogen form (50-100 mesh, 8.00 g), and methanol (180.0 mL) were added in a round bottom flask 250 mL equipped with a magnetic stirrer. After that, the suspended mixture was stirred at room temperature for 7 h under argon. The resin was then filtered out and washed with methanol. The filtered solution was concentrated under reduced pressure to yield the yellowish oil in quantitative yield. HRMS analysis (C 9

Synthesis of Diethyl (3-Azidopropyl)phosphonate (Azido-phosphonate)
Diethyl (3-bromopropyl)phosphonate (5.00 g, 19.31 × 10 −3 mol) and DMF (15.0 mL) were added to a round-bottom flask and stirred at room temperature under argon. Then, sodium azide (NaN 3 , 3.00 g, 46.15 × 10 −3 mol) was slowly added into the flask containing the reaction mixture. The suspension was stirred for 1 h at room temperature and then for 42 h at 40 • C. Multiple filtrations were performed to remove the solid from the mixture. The solution was then concentrated under reduced pressure to obtain the yellow oil (3.46 g, 97% w/w in DMF). 1

Ring-Opening Polymerization of 4
Benzyl alcohol (BnOH, 24.3 mg, 2.25 × 10 −4 mol), phosphonate monomer 4 (2.00 g, 6.76 × 10 −3 mol), and thiourea (TU, 106 mg, 2.86 × 10 −4 mol) were placed in a vial equipped with a magnetic stirrer, sealed with a rubber septum and flushed under argon. Under argon, the vial was filled with DCM (3.0 mL) and stirred to obtain a homogeneous solution. Then, a deoxygenated solution of DBU catalyst (41.0 mg, 2.70 × 10 −4 mol) in DCM (1.0 mL) was injected quickly into the vial. The polymerization was launched and carried out at room temperature in the presence of argon. After 100 min, benzoic acid (45.0 mg) was added to the vial to stop the polymerization. The crude product was dissolved with acetone. This solution was dialyzed using a dialysis membrane (3500 Da) against acetone/water (1/3 in v/v). The polymer was recovered by lyophilization and dried at 45 • C to obtain a gummy solid with M n,SEC = 2500 g·mol −1 , Ð = 1.22, and DP n,NMR = 23. 1

Synthesis of Phosphonate-Functionalized Cyclic Carbonate Monomer
To synthesize the phosphonate-functionalized polycarbonate, a novel cyclic carbonate monomer bearing a phosphonate group was synthesized from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) as the starting substance according to the synthetic route shown in Scheme 1.

Synthesis of Phosphonate-Functionalized Cyclic Carbonate Monomer
To synthesize the phosphonate-functionalized polycarbonate, a novel cyclic carbonate monomer bearing a phosphonate group was synthesized from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) as the starting substance according to the synthetic route shown in Scheme 1. The synthesis of 2-(dimethoxyphosphoryl)ethyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate monomer (phosphonate-carbonate, 4) was achieved in four steps with an average yield of 28.6%. After purification, the structure of the product was verified using NMR spectroscopy. Figure 1A depicts the 1 H NMR spectrum of 4, which exhibits characteristic signals at 4.19 ppm and 4.71 ppm (labeled (b), (c)), corresponding to the methylene of cyclic carbonate (-CH2OC(O)OCH2-) with the signal at 3.76 ppm, corresponding to the methoxy of phosphonate (-PO(OCH3)2). In addition, the presence of carbonate and phosphonate functionalities was also checked using 13 C and 31 P NMR spectroscopies with the presence of the carbonyl signal at 147.36 ppm as well as the phosphorous signal at 28.61 ppm, respectively ( Figure 1B,C). These results demonstrate the effective synthesis of phosphonate-containing cyclic carbonate 4.
Owing to the six-membered cyclic carbonate with high reactivity toward ring-opening polymerization, 4 could be an excellent monomer to synthesize well-defined phosphonate-functionalized polycarbonate. As a result, we attempted to polymerize 4 using the organocatalyzed ring-opening polymerization (ROP) technique to produce the corresponding phosphonate-functionalized polycarbonate. The synthesis of 2-(dimethoxyphosphoryl)ethyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate monomer (phosphonate-carbonate, 4) was achieved in four steps with an average yield of 28.6%. After purification, the structure of the product was verified using NMR spectroscopy. Figure 1A

ROP Synthesis of Well-Defined Phosphonate-Functionalized (Co)polycarbonates
Due to its catalytic efficiency in the ROP of a wide range of cyclic monomers, DBU has been widely used, and is one of the most desired catalysts for ROP of functional cyclic carbonates [16,22]. In combination with the DBU catalyst, the addition of thiourea TU Owing to the six-membered cyclic carbonate with high reactivity toward ring-opening polymerization, 4 could be an excellent monomer to synthesize well-defined phosphonatefunctionalized polycarbonate. As a result, we attempted to polymerize 4 using the organocatalyzed ring-opening polymerization (ROP) technique to produce the corresponding phosphonate-functionalized polycarbonate.

ROP Synthesis of Well-Defined Phosphonate-Functionalized (Co)polycarbonates
Due to its catalytic efficiency in the ROP of a wide range of cyclic monomers, DBU has been widely used, and is one of the most desired catalysts for ROP of functional cyclic carbonates [16,22]. In combination with the DBU catalyst, the addition of thiourea TU (co)catalyst serves as an activating monomer additive by increasing the electrophilicity of the carbonyl groups in cyclic carbonate monomers [23,24]. This favors the addition of a nucleophile to the monomer over the polymer backbone, accelerating the polymerization and minimizing the transesterification at high monomer conversion during the ROP [25]. Hence, the ROP of 4 was performed in the presence of the DBU/TU as catalytic systems and benzyl alcohol (BnOH) as the initiator in DCM to obtain the corresponding phosphonate functionalized-polycarbonate (Scheme 2) ( Table 1, entry 1).

ROP Synthesis of Well-Defined Phosphonate-Functionalized (Co)polycarbonates
Due to its catalytic efficiency in the ROP of a wide range of cyclic monomers, DBU has been widely used, and is one of the most desired catalysts for ROP of functional cyclic carbonates [16,22]. In combination with the DBU catalyst, the addition of thiourea TU (co)catalyst serves as an activating monomer additive by increasing the electrophilicity of the carbonyl groups in cyclic carbonate monomers [23,24]. This favors the addition of a nucleophile to the monomer over the polymer backbone, accelerating the polymerization and minimizing the transesterification at high monomer conversion during the ROP [25]. Hence, the ROP of 4 was performed in the presence of the DBU/TU as catalytic systems and benzyl alcohol (BnOH) as the initiator in DCM to obtain the corresponding phosphonate functionalized-polycarbonate (Scheme 2) ( Table 1, entry 1).

Scheme 2.
Organocatalyzed ROP of 4 with DBU/TU as the catalytic system in dichloromethane.
As expected, the polymerization of 4 was successful, with 90% of the monomer converted into polymer after 100 min. Monomer conversion was calculated based on the comparison of 1 H NMR integral intensities between the methylene signal of cycle carbonate at 4.71 ppm and signal at 3.71-3.80 ppm due to the methoxy group (-PO(OCH3)2) of the monomer and the polymers formed. Furthermore, the formation and structure of phosphonate-functionalized polycarbonate 5 (poly[(4)], Scheme 2) were validated using 1 H and 31 P NMR spectroscopies. The 1 H NMR spectrum of 5 ( Figure 2) displays the characteristic polymer signals at 7.31-7.78 ppm and 5.13 ppm due to the benzyl extremity (C6H5CH2-, labeled (a) and (b)), followed by the polymer backbone signal at 4.12-4.50 ppm, and the methoxy (-PO(OCH3)2, labeled (h, h')) at 3.71-3.80 ppm. The intensity integration ratio of these signals served to determine the degree of polymerization (DPn,NMR = 23) and thus the average number of molecular weight by NMR (Mn,NMR = 6920 g·mol −1 ). The good correlation between the Mn,NMR, and its theoretical value (Mn,th = 8100 g·mol −1 ) demonstrates the high polymer chain-end functionality and the control character of the polymerization.   As expected, the polymerization of 4 was successful, with 90% of the monomer converted into polymer after 100 min. Monomer conversion was calculated based on the comparison of 1 H NMR integral intensities between the methylene signal of cycle carbonate at 4.71 ppm and signal at 3.71-3.80 ppm due to the methoxy group (-PO(OCH 3 ) 2 ) of the monomer and the polymers formed. Furthermore, the formation and structure of phosphonate-functionalized polycarbonate 5 (poly[(4)], Scheme 2) were validated using 1 H and 31 P NMR spectroscopies. The 1 H NMR spectrum of 5 (Figure 2) displays the characteristic polymer signals at 7.31-7.78 ppm and 5.13 ppm due to the benzyl extremity (C 6 H 5 CH 2 -, labeled (a) and (b)), followed by the polymer backbone signal at 4.12-4.50 ppm, and the methoxy (-PO(OCH 3 ) 2 , labeled (h, h')) at 3.71-3.80 ppm. The intensity integration ratio of these signals served to determine the degree of polymerization (DP n,NMR = 23) and thus the average number of molecular weight by NMR (M n,NMR = 6920 g·mol −1 ). The good correlation between the M n,NMR , and its theoretical value (M n,th = 8100 g·mol −1 ) demonstrates the high polymer chain-end functionality and the control character of the polymerization. Additionally, the intact phosphonate group through the polymerization was validated by the phosphorous signals at 29.15-29.96 ppm on the 31 P NMR spectrum ( Figure 2). Additionally, the intact phosphonate group through the polymerization was validated by the phosphorous signals at 29.15-29.96 ppm on the 31 P NMR spectrum (Figure 2).  The presence of several phosphorous peaks indicates that the transesterification on phosphonate groups occurred during the polymerization. Indeed, the intramolecular and intermolecular transesterification reactions are frequently observed during the ROP of cyclic phosphoester monomers [26][27][28]. In our case, a possible transesterification through dimethyl phosphonate function could take place due to lower steric hindrance of the methoxy group (-OCH3). In addition, because of the high affinity of the TU catalyst with carbonyl (-C=O) and -P=O groups that are both present in 4, this may result in a competitive interaction between these two functionalities and the TU. Such interaction could then decrease the performance of the TU catalyst. Despite the transesterification, the SEC analysis ( Figure 3) reveals a unimodal and narrow dispersity corresponding to a polymer with Mn,SEC equal to 2500 g·mol −1 . Moreover, the low dispersity value (Ð = 1.22) indicates the homogeneity of the resulting polymer chains. The difference value between the Mn,SEC and Mn,th could be due to the different hydrodynamic volumes of polymers and poly(methyl methacrylate) standards used for calibration. All these results demonstrate, for the first time, the successful synthesis of well-defined phosphonate-functionalized polycarbonate using organo-catalyzed ROP. The presence of several phosphorous peaks indicates that the transesterification on phosphonate groups occurred during the polymerization. Indeed, the intramolecular and intermolecular transesterification reactions are frequently observed during the ROP of cyclic phosphoester monomers [26][27][28]. In our case, a possible transesterification through dimethyl phosphonate function could take place due to lower steric hindrance of the methoxy group (-OCH 3 ). In addition, because of the high affinity of the TU catalyst with carbonyl (-C=O) and -P=O groups that are both present in 4, this may result in a competitive interaction between these two functionalities and the TU. Such interaction could then decrease the performance of the TU catalyst. Despite the transesterification, the SEC analysis ( Figure 3) reveals a unimodal and narrow dispersity corresponding to a polymer with M n,SEC equal to 2500 g·mol −1 . Moreover, the low dispersity value (Ð = 1.22) indicates the homogeneity of the resulting polymer chains. The difference value between the M n,SEC and M n,th could be due to the different hydrodynamic volumes of polymers and poly(methyl methacrylate) standards used for calibration. All these results demonstrate, for the first time, the successful synthesis of well-defined phosphonate-functionalized polycarbonate using organo-catalyzed ROP.   Table 1.
As a versatile method, the phosphonate-functionalized polycarbonate could directly be obtained using ROP of 4 or via ring-opening copolymerization of 4 with another comonomer. In particular, copolymerization has been employed to combine the properties of different materials to create novel materials. Copolymerization is therefore a simple method for expanding the series of biodegradable phosphonate-functionalized PC. In addition, we believe that the presence of comonomer units in the polymer backbone can significantly increase the steric hindrance surrounding the phosphonate groups, thereby limiting transesterification through the methoxy of phosphonates.
Then, the polymerization of 4 and alkyne-based cyclic carbonate (MPC) as a comon-  Table 1.
As a versatile method, the phosphonate-functionalized polycarbonate could directly be obtained using ROP of 4 or via ring-opening copolymerization of 4 with another comonomer. In particular, copolymerization has been employed to combine the properties of different materials to create novel materials. Copolymerization is therefore a simple method for expanding the series of biodegradable phosphonate-functionalized PC.
In addition, we believe that the presence of comonomer units in the polymer backbone can significantly increase the steric hindrance surrounding the phosphonate groups, thereby limiting transesterification through the methoxy of phosphonates.
Then, the polymerization of 4 and alkyne-based cyclic carbonate (MPC) as a comonomer in different molar fractions was carried out with DBU/TU as the catalytic system at room temperature in DCM (Scheme 3). These polymerization conditions and the resulting polymer properties are summarized in Table 1 (entries 2 and 3). As a versatile method, the phosphonate-functionalized polycarbonate could directly be obtained using ROP of 4 or via ring-opening copolymerization of 4 with another comonomer. In particular, copolymerization has been employed to combine the properties of different materials to create novel materials. Copolymerization is therefore a simple method for expanding the series of biodegradable phosphonate-functionalized PC. In addition, we believe that the presence of comonomer units in the polymer backbone can significantly increase the steric hindrance surrounding the phosphonate groups, thereby limiting transesterification through the methoxy of phosphonates.
Then, the polymerization of 4 and alkyne-based cyclic carbonate (MPC) as a comonomer in different molar fractions was carried out with DBU/TU as the catalytic system at room temperature in DCM (Scheme 3). These polymerization conditions and the resulting polymer properties are summarized in Table 1 (entries 2 and 3). The successful copolymerization synthesis of phosphonate-functionalized (co)polycarbonates (poly[(4)-co-MPC], Scheme 3) was confirmed using SEC analysis with Mn,SEC equal to 3800 g·mol −1 and 4400 g·mol −1 and Đ values around 1.3 (Table 1, entries 2-3). The structure of the novel copolymers was confirmed with the appearance of typical signals such as the methoxy (labeled (h)) due to 4 units at 3.71-3.81 ppm along with the methylene (labeled (i)) signals at 4.67-4.78 ppm, attributed to MPC units in the 1 H NMR spectrum ( Figure 4). The composition of these resulting polymers was also identified as poly[(4)21co-MPC21] and poly[(4)10-co-MPC33] using 1 H NMR analysis of polymer chain-end. In addition, Table 1 shows the excellent correlation between the Mn,NMR and theoretical values (Mn,th), indicating the controlled ROP process. Moreover, a low transesterification was confirmed by observing the intensity of phosphorous signals at 29.14 ppm and 30.06 ppm on the 31 P NMR spectrum (top-right, Figure 4). These data demonstrate the successful copolymerization synthesis of well-defined phosphonate-functionalized (co)polycarbonates. Moreover, the convincing results indicate that the copolymerization of 4 with other monomers could be a relevant strategy for the development of novel phosphorous materials based on phosphonate-functionalized polycarbonates. The successful copolymerization synthesis of phosphonate-functionalized (co)polycarbonates (poly[(4)-co-MPC], Scheme 3) was confirmed using SEC analysis with M n,SEC equal to 3800 g·mol −1 and 4400 g·mol −1 and Ð values around 1.3 (Table 1, entries 2-3). The structure of the novel copolymers was confirmed with the appearance of typical signals such as the methoxy (labeled (h)) due to 4 units at 3.71-3.81 ppm along with the methylene (labeled (i)) signals at 4.67-4.78 ppm, attributed to MPC units in the 1 H NMR spectrum (Figure 4). The composition of these resulting polymers was also identified as poly[(4) 21 -co-MPC 21 ] and poly[(4) 10 -co-MPC 33 ] using 1 H NMR analysis of polymer chain-end. In addition, Table 1 shows the excellent correlation between the M n,NMR and theoretical values (M n,th ), indicating the controlled ROP process. Moreover, a low transesterification was confirmed by observing the intensity of phosphorous signals at 29.14 ppm and 30.06 ppm on the 31 P NMR spectrum (top-right, Figure 4). These data demonstrate the successful copolymerization synthesis of well-defined phosphonate-functionalized (co)polycarbonates. Moreover, the convincing results indicate that the copolymerization of 4 with other monomers could be a relevant strategy for the development of novel phosphorous materials based on phosphonate-functionalized polycarbonates.

Post-Polymerization Synthesis of Phosphonate-Functionalized Polycarbonate
Although the synthesis of well-defined phosphonate-functionalized polycarbonates has been successfully demonstrated using (co)polymerizations of 4, the multi-step monomer synthesis and the transesterification of the phosphonate group during the polymerization are the major drawbacks when it comes to considering a scale-up. These limitations

Post-Polymerization Synthesis of Phosphonate-Functionalized Polycarbonate
Although the synthesis of well-defined phosphonate-functionalized polycarbonates has been successfully demonstrated using (co)polymerizations of 4, the multi-step monomer synthesis and the transesterification of the phosphonate group during the polymerization are the major drawbacks when it comes to considering a scale-up. These limitations motivated us to develop a robust and highly efficient post-polymerization method to prepare the phosphonate-functionalized PC. Unlike the low yield of the previously mentioned "amine-acid" reaction, the "click" reaction has emerged as the most efficient and powerful reaction for the synthesis of functional polymers [29][30][31]. "Click" chemistry was chosen to synthesize the phosphonate-functionalized PC using the reaction between an alkynefunctionalized polycarbonate based on poly(MPC) 46 (M n,SEC = 4200 g·mol −1 , Ð = 1.4) and an azido-phosphonate compound in the presence of CuBr and PMDETA as the catalyst system and DMF (Scheme 4).

Post-Polymerization Synthesis of Phosphonate-Functionalized Polycarbonate
Although the synthesis of well-defined phosphonate-functionalized polycarbonates has been successfully demonstrated using (co)polymerizations of 4, the multi-step monomer synthesis and the transesterification of the phosphonate group during the polymerization are the major drawbacks when it comes to considering a scale-up. These limitations motivated us to develop a robust and highly efficient post-polymerization method to prepare the phosphonate-functionalized PC. Unlike the low yield of the previously mentioned "amine-acid" reaction, the "click" reaction has emerged as the most efficient and powerful reaction for the synthesis of functional polymers [29][30][31]. "Click" chemistry was chosen to synthesize the phosphonate-functionalized PC using the reaction between an alkyne-functionalized polycarbonate based on poly(MPC)46 (Mn,SEC = 4200 g·mol −1 , Ð = 1.4) and an azido-phosphonate compound in the presence of CuBr and PMDETA as the catalyst system and DMF (Scheme 4). The SEC trace of the resulting product shifted to the lower retention volume, indicating the higher molecular weight of the polymer product and also the successful grafting of azido-phosphonate on the polymer backbone ( Figure 5A). In addition, the existence of a single phosphorous signal at 30.06 ppm on the 31 P NMR spectrum confirmed the effective incorporation of phosphonate into poly(MPC)46 chains ( Figure 5B). The SEC trace of the resulting product shifted to the lower retention volume, indicating the higher molecular weight of the polymer product and also the successful grafting of azido-phosphonate on the polymer backbone ( Figure 5A). In addition, the existence of a single phosphorous signal at 30.06 ppm on the 31 P NMR spectrum confirmed the effective incorporation of phosphonate into poly(MPC) 46 chains ( Figure 5B). Moreover, the overlaid 1 H NMR spectra of poly(MPC)46 before and after the reaction ( Figure 6) upheld the formation of the phosphonate-functionalized poly(MPC)46 product with the appearance of the novel signal at 8.08 ppm (labeled (g)), characteristic of the proton of cyclic triazole along with the methylene signals (labeled (h), (i) and (j)) due to grafted azido-phosphonate on the polymer backbone. The functionality yield was also determined to be above 95%. All these results confirm the high efficiency of the "click" reaction to graft the azido-phosphonate on the polycarbonate backbone as well as the successful synthesis of phosphonate-functionalized polycarbonate. Moreover, the overlaid 1 H NMR spectra of poly(MPC) 46 before and after the reaction ( Figure 6) upheld the formation of the phosphonate-functionalized poly(MPC) 46 product with the appearance of the novel signal at 8.08 ppm (labeled (g)), characteristic of the proton of cyclic triazole along with the methylene signals (labeled (h), (i) and (j)) due to grafted azido-phosphonate on the polymer backbone. The functionality yield was also determined to be above 95%. All these results confirm the high efficiency of the "click" reaction to graft the azido-phosphonate on the polycarbonate backbone as well as the successful synthesis of phosphonate-functionalized polycarbonate.
( Figure 6) upheld the formation of the phosphonate-functionalized poly(MPC)46 product with the appearance of the novel signal at 8.08 ppm (labeled (g)), characteristic of the proton of cyclic triazole along with the methylene signals (labeled (h), (i) and (j)) due to grafted azido-phosphonate on the polymer backbone. The functionality yield was also determined to be above 95%. All these results confirm the high efficiency of the "click" reaction to graft the azido-phosphonate on the polycarbonate backbone as well as the successful synthesis of phosphonate-functionalized polycarbonate. Figure 6. Overlaid 1 H NMR spectra of poly(MPC)46 in CDCl3 before and after the "click" reaction with azido-phosphonate in acetone D6.

Conclusions
We have successfully demonstrated two strategies for synthesizing polycarbonatebearing pendant phosphonate groups. For the first time, a well-defined phosphonatefunctionalized polycarbonate was directly synthesized using organocatalyzed ROP of new phosphonate containing cyclic carbonate. The copolymerization of phosphorus monomer was also performed to access the various structures of polycarbonate-containing phosphonate groups. Furthermore, copolymerization could be a useful approach for

Conclusions
We have successfully demonstrated two strategies for synthesizing polycarbonatebearing pendant phosphonate groups. For the first time, a well-defined phosphonatefunctionalized polycarbonate was directly synthesized using organocatalyzed ROP of new phosphonate containing cyclic carbonate. The copolymerization of phosphorus monomer was also performed to access the various structures of polycarbonate-containing phosphonate groups. Furthermore, copolymerization could be a useful approach for limiting the transesterification of the dimethyl phosphonate group. Finally, "click" chemistry was effectively used to graft the phosphonate group on the polycarbonate backbone. This post-modification approach could be a convenient way to avoid the undesirable transesterification of the phosphonate group during the ROP process.